1. Field of the Invention
The present invention relates to a vaporizer for vaporizing a liquid raw material, a semiconductor device manufactured by using the vaporizer, and a method of manufacturing the semiconductor device by using the vaporizer. More particularly, the vaporizer is to be used for a CVD (Chemical Vapor Deposition) apparatus in the field of a semiconductor manufacturing apparatus.
2. Description of the Background Art
In recent years, the integration of semiconductor memories and devices has rapidly been enhanced in order to increase the processing speed of the device, to reduce power consumption and to cut down costs. However, even if the integration is enhanced, a capacitor to be a component of a DRAM (Dynamic Random Access Memory) requires a prescribed capacity. For this reason, it is necessary to reduce the thickness of a capacitor dielectric layer.
However, reduction in the film thickness of silicon dioxide (SiO2) which has been used as the capacitor dielectric layer has almost reached the limit. Consequently, vigorous studies and developments have been made to utilize a material having a high dielectric constant as the material of the capacitor dielectric layer and a metal material as the material of a capacitor electrode, in order to change the material of the capacitor dielectric layer to increase the dielectric constant. More specifically, tantalum oxide, lead zircon titanate (PZT), lead lanthanum zircon titanate (PLZT), strontium titanate (ST), barium titanate (BT), barium strontium titanate ((Ba, Sr) TiO3 which will be hereinafter referred to as xe2x80x9cBSTxe2x80x9d) and the like have been studied as the material having a high dielectric constant, and platinum (Pt), ruthenium (Ru) and the like have been studied as the metal material.
In order to form the thin films of the material having a high dielectric constant and the metal material on the pattern of a semiconductor device having a difference in height, it is the most advantageous that the film formation should be carried out by a CVD method having excellent attachment properties to a substance having a complicated shape. However, there is a big problem in that no material has stable and excellent vaporization characteristic for a CVD raw material to form a thin film having a high dielectric constant and a metal thin film.
Under the circumstances, the present inventors have proposed a CVD raw material in Japanese Patent Layingxe2x80x94Open No. 7-268634 in which a conventional solid raw material is dissolved in an organic solvent, that is, tetrahydrofuran (C4H8O, hereinafter referred to as xe2x80x9cTHFxe2x80x9d) to remarkably enhance vaporization properties. However, even if a thin film having a high dielectric constant is formed with this raw material by using a conventional CVD apparatus for a liquid raw material, for example, for the formation of a SiO2 film, good results cannot be obtained. Therefore, the present inventors have further proposed a CVD apparatus for a liquid raw material which can fully vaporize a liquid raw material to be supplied stably to a reaction chamber (Japanese Patent Layingxe2x80x94Open No. 8-186103).
FIG. 8 is a typical view schematically showing a solution vaporizing CVD apparatus for forming a thin film having a high dielectric constant which has been described in Japanese Patent Layingxe2x80x94Open No. Hei 8-186103. With reference to FIG. 8, the conventional CVD apparatus mainly has a liquid raw material vaporizer 101, liquid raw material vessels 102 to 105, a pressure pipe 106, liquid raw material flow controllers 107 to 110, a carrier gas supply pipe 111, a carrier gas flow controller 112, a connecting pipe 113, an oxidant supply pipe 114, a raw material gas transport pipe 115, a transport pipe heater 116, a reaction chamber 117 and a substrate heater 118.
Each of the four liquid raw material vessels 102 to 105 is connected to the pressure pipe 106, and is connected to the connecting pipe 113 through each of the liquid raw material flow controllers 107 to 110. The carrier gas supply pipe 111 is also connected to the connecting pipe 113 through the carrier gas flow controller 112.
The connecting pipe 113 is connected to a raw material supply pipe 123 of the liquid raw material vaporizer 101. The raw material gas transport pipe 115 extended toward the reaction chamber 117 is connected to the liquid raw material vaporizer 101. Moreover, the oxidant supply pipe 114 is provided to be extended toward the reaction chamber 117. There are provided the transport pipe heater 116 for heating the raw material gas transport pipe 115 and a heater for heating the oxidant supply pipe 114.
The substrate heater 118 for heating and holding a semiconductor substrate 119 is held in the reaction chamber 117.
Next, the operation of a conventional solution vaporizing CVD apparatus will be described.
A carrier gas flows from the carrier gas supply pipe 111 to the connecting pipe 113 with its a flow rate adjusted by the carrier gas flow controller 112. A solution raw material in the liquid raw material vessels 102 to 105 is pressurized by the pressure pipe 106 and the flow rate thereof is adjusted by the liquid raw material flow controllers 107 to 110. Then, the solution material is supplied to the connecting pipe 113 and is sprayed into the liquid raw material vaporizer 101.
The liquid raw material sprayed into the liquid raw material vaporizer 101 is vaporized in the liquid raw material vaporizer 101. The vaporized gas (raw material gas) is supplied into the reaction chamber 117 through the raw material gas transport pipe 115 heated by the transport pipe heater 116. The raw material gas reacts, in the reaction chamber 117, with an oxidant supplied from the oxidant supply pipe 114, and a thin film having a high dielectric constant or a metal thin film is formed on the semiconductor substrate 119 heated by the substrate heater 118.
An organic solvent THF and a solution raw material are provided in each of the liquid raw material vessels 102 to 105. The reaction chamber 117 is set at a pressure of approximately 133 Pa to approximately 1330 Pa in the O2 atmosphere. A film is formed, with the heater set temperature of 400 to 600xc2x0 C.
However, it has been found that a thin film having a high dielectric constant and a metal thin film cannot always be formed stably by using the solution vaporizing CVD apparatus. Actually, there have been the following problems. More specifically, foreign matters fall onto a semiconductor substrate (wafer), and a film forming rate, film properties (film composition and crystallinity) and electrical characteristics vary for each film formation.
The present inventors have investigated the cause. As a result, it has been found that the above-mentioned drawbacks are caused by a solid component such as an organic metal compound deposited from a liquid raw material in the liquid raw material vaporizer 101, which will be specifically described below with reference to the drawings.
FIG. 9 is a sectional view schematically showing the structure of a conventional liquid raw material vaporizer. With reference to FIG. 9, the liquid raw material vaporizer 101 includes a vaporizer body 120, an upper vaporizer cover 121, a rod heater 122 and a raw material supply pipe 123. The vaporizer body 120 and the upper vaporizer cover 121 constitute a vaporizing chamber, in which the rod heater 122 is embedded. The raw material supply pipe 123 for supplying a mixture of a liquid raw material and a carrier gas into the vaporizing chamber is connected to the upper vaporizer cover 121. Moreover, the vaporizer body 120 is provided with a vaporizing chamber outlet for discharging the vaporized raw material. A raw material gas transport pipe 115 for introducing the vaporized raw material to a reaction chamber is connected to the outlet of the vaporizing chamber. A transport pipe heater 116 is provided around the vaporizer outlet portion and the raw material gas transport pipe 115.
The vaporizer body 120 and the upper vaporizer cover 121 are formed of a metal, for example, a metal having a high thermal conductivity such as aluminum (Al) or copper (Cu). Moreover, a tube formed of PTFE (polytetrafluoroethylene) or polyimide is used for the raw material supply pipe 123, and a stainless tube is used for the raw material gas transport pipe 115.
In such a liquid raw material vaporizer 101, the liquid raw material is scattered or sprayed together with a carrier gas from a terminating and of the raw material supply pipe 123 into the vaporizing chamber. Then, the liquid raw material supplied into the vaporizing chamber collides with the internal wall of the vaporizing chamber. At this time, the vaporizer body 120 and the upper vaporizer cover 121 are heated by the rod heater 122. Therefore, the liquid raw material colliding with the internal wall of the vaporizing chamber is vaporized instantaneously. The liquid raw material thus vaporized (which will be hereinafter referred to as a xe2x80x9craw material gasxe2x80x9d) is discharged from the vaporizing chamber outlet portion and is supplied to the reaction chamber.
However, the vaporizer body 120 and the upper vaporizer cover 121 are heated by the rod heater 122. Therefore, the heat is also transmitted to the raw material supply pipe 123 connected to the upper vaporizer cover 121 so that the temperature of the raw material supply pipe 123 is raised. As a result, the solvent of the liquid raw material is partially vaporized in the raw material supply pipe 123 in some cases. When the solvent is thus vaporized partially, a part of an organic metal compound to be a solute dissolved in the liquid raw material is deposited as a solid in the raw material supply pipe 123 in some cases. The deposited organic chemical metal to be the raw material of a CVD film (which will be hereinafter referred to as a vaporization residue) is accumulated in the vaporizing chamber or the raw material supply pipe 123. Such an accumulated vaporization residue slightly changes the temperature of the internal wall of the vaporizing chamber. As a result, the vaporizing characteristics of the liquid raw material are affected. Consequently, the raw material gas cannot be fed stably from the vaporizing chamber to the reaction chamber 117. Thus, there is a problem in that the characteristics of the CVD film are deteriorated.
Moreover, the vaporization residue accumulated in the vaporizing chamber and the like is discharged as a powder solid component together with the vaporized raw material from the vaporizing chamber outlet portion and reaches the reaction chamber 117 in some cases. In these cases, the vaporization residue would be incorporated as a foreign matter into the CVD film in the reaction chamber 117. Consequently, a device using such a CVD film sometimes operates defectively.
If the above-mentioned CVD apparatus is used for a long period of time, the temperature of the internal wall of the vaporizing chamber is lowered by the vaporization residue accumulated in the vaporization chamber, affecting the vaporizing characteristics of the liquid raw material, so that more vaporization residues are increasingly accumulated in the vaporizer. For this reason, it is hard to stably obtain a CVD film having excellent properties, for a long period of time.
It is an object of the present invention to provide a liquid raw material vaporizer capable of suppressing the generation of a vaporization residue and of forming a film having stable properties.
It is another object of the present invention to provide a semiconductor device having a CVD film having stable properties and a method of manufacturing the semiconductor device.
A liquid raw material vaporizer according to the present invention serves to vaporize a liquid raw material obtained by dissolving an organic metal complex in a solvent, including a raw material supply pipe, a vaporizing chamber and suppressing means. The raw material supply pipe serves to guide the liquid raw material. The vaporizing chamber is connected to the raw material supply pipe and serves to heat and vaporize the liquid raw material introduced from the raw material supply pipe. The suppressing means is fixed to at least one of the vaporizing chamber and the raw material supply pipe and serves to suppress transmission of heat from the vaporizing chamber to the raw material supply pipe.
In the liquid raw material vaporizer according to the present invention, it is possible to suppress the transmission of heat from the vaporizing chamber to the raw material supply pipe through the suppressing means. Consequently, the temperature of the raw material supply pipe can be prevented from being raised. Consequently, the problem that a solvent is partially vaporized in the raw material supply pipe portion and a part of an organic metal compound is deposited as a solid can be prevented. In other words, the generation of a vaporization residue can be suppressed.
Consequently, the change in the temperature of the internal wall of the vaporizing chamber caused by the vaporization residue can be prevented. Therefore, it is possible to prevent the film characteristics from being deteriorated by the change in the temperature of the internal wall.
Moreover, it is possible to prevent the vaporization residue from being incorporated as a foreign matter in the film. Thus, it is possible to obtain a film having excellent characteristics.
Furthermore, decrease in the temperature of the internal wall of the vaporizing chamber caused by the vaporization residue can be prevented. Consequently, a vicious circle caused by the accumulation of the vaporization residue can also be prevented. Thus, a film having excellent characteristics can easily be obtained stably for a long period of time.
In the liquid raw material vaporizer, preferably, the suppressing means is a heat radiation preventing member provided on an external wall of the vaporizing chamber and formed of a material having a thermal emissivity lower than that of the vaporizing chamber.
The heat radiation preventing member can prevent heat from being radiated from the surface of the external wall of the vaporizing chamber. Consequently, the raw material supply pipe can be prevented from being heated by the radiation.
In the liquid raw material vaporizer, preferably, a material of the heat radiation preventing member is at least one selected from the group consisting of glass, polyimide, fiber, Teflon and a metal having a surface oxidized.
By selecting these materials, it is possible to set the thermal emissivity of the thermal radiation preventing member to be lower than that of the vaporizing chamber.
In the liquid raw material vaporizer, preferably, the suppressing means is a heat absorption preventing member provided to surround a peripheral surface of the raw material supply pipe and formed of a material which absorbs less heat than the raw material supply pipe.
By the heat absorption preventing member, it is possible to prevent the absorption of the heat radiated from the surface of the external wall of the vaporizing chamber. Consequently, it is possible to prevent the raw material supply pipe from being heated.
In the liquid raw material vaporizer, preferably, a material of the heat absorption preventing member is at least one selected from the group consisting of aluminum, copper, nickel and stainless steel.
By selecting these materials, it is possible to make the heat absorption preventing member absorb less heat than the raw material supply pipe.
In the liquid raw material vaporizer, preferably, the suppressing means is a heat insulating member provided between the vaporizing chamber and the raw material supply pipe and formed of a material having a thermal conductivity lower than that of the vaporizing chamber.
By the heat insulating member, the transmission of the heat from the vaporizing chamber to the raw material supply pipe can be blocked. Consequently, it is possible to prevent the raw material supply pipe from being heated.
In the liquid raw material vaporizer, preferably, the heat insulating member has a structure in which multiple heat insulating layers are superposed.
Consequently, the capability of blocking the transmission of the heat from the vaporizing chamber to the raw material supply pipe can be enhanced. Thus, the heating of the raw material supply pipe can be prevented still more.
In the liquid raw material vaporizer, preferably, a material of the heat insulating member is at least one selected from the group consisting of celluloid, polyimide, Teflon, fluoro rubber and silicone rubber.
By selecting these materials, it is possible to set the thermal conductivity of the heat insulating member to be lower than that of the vaporizing chamber.
A semiconductor device according to the present invention has a capacitor in which a capacitor dielectric layer including a material having a high dielectric constant is interposed between a pair of electrodes containing a metal, wherein a standard deviation of film thickness stability of at least one of the capacitor dielectric layer and the pair of electrodes is 3% or less.
The semiconductor device according to the present invention includes a capacitor electrode or a capacitor dielectric layer having a stable thickness of which standard deviation of film thickness stability is 3% or less.
The xe2x80x9cstandard deviation of film thickness stabilityxe2x80x9d is calculated based on a value (deviation) obtained by subtracting a mean value (an expected value) from a thickness (a measured value) measured at a plurality of portions of the capacitor dielectric layer or the capacitor electrode which are optionally selected from the measured value. The xe2x80x9cstandard deviation of film thickness stabilityxe2x80x9d represented by s is calculated based on the following equation.
S=(1/n)xcexa3(xixe2x88x92{overscore (x)})2xe2x80x83xe2x80x83(1)
n: number of measured portions
xi: measured value
{overscore (x)}: mean value
In the semiconductor device, preferably, a material of the capacitor dielectric layer includes at least one selected from the group consisting of tantalum oxide, lead zircon titanate, lead lanthanum zircon titanate, strontium titanate, barium titanate and barium strontium titanate.
By selecting these materials, a capacitor dielectric layer having a high dielectric constant can be obtained.
In the semiconductor device, preferably, the capacitor dielectric layer includes at least one of lead zircon titanate, lead lanthanum zircon titanate, and barium strontium titanate, and a standard deviation of stability of a composition ratio of the capacitor dielectric layer is 5% or less.
Consequently, it is possible to obtain a semiconductor device including a capacitor dielectric layer having a stable composition ratio.
A xe2x80x9cstandard deviation of stability of a composition ratioxe2x80x9d is calculated from a value (deviation) by subtracting a population mean value (an expected value) from a composition ratio (a measured value) measured at a plurality of portions of the capacitor dielectric layer which are optionally selected from the measured value, and is obtained by the same equation as in the equation (1).
In the semiconductor device, preferably, a material of at least one of the pair of electrodes includes at least one of platinum and ruthenium.
By selecting these materials, the capacitor dielectric layer interposed between the electrodes can have a high dielectric constant.
The present invention provides a method of manufacturing a semiconductor device, including the steps of vaporizing a liquid raw material having an organic metal complex dissolved in a solvent by using a liquid raw material vaporizer and producing a vaporized raw material, introducing the vaporized raw material into a reaction chamber holding a semiconductor substrate therein and using the vaporized raw material, forming at least one of a capacitor electrode and a capacitor dielectric layer on the semiconductor substrate by a chemical vapor deposition method. The liquid raw material vaporizer includes a raw material supply pipe, a vaporizing chamber and suppressing means. The raw material supply pipe serves to guide the liquid raw material. The vaporizing chamber is connected to the raw material supply pipe and serves to heat and vaporize the liquid raw material introduced from the raw material supply pipe. The suppressing means is fixed to at least one of the vaporizing chamber and the raw material supply pipe and serves to suppress transmission of heat from the vaporizing chamber to the raw material supply pipe.
In the method of manufacturing a semiconductor device according to the present invention, the transmission of heat from the vaporizing chamber to the raw material supply pipe can be controlled in the liquid raw material vaporizer. Consequently, it is possible to manufacture a semiconductor device including a capacitor electrode or a capacitor dielectric layer having a stable thickness of which standard deviation of film thickness stability is 3% or less.
In the method of manufacturing a semiconductor device, preferably, the organic metal complex includes at least one selected from the group consisting of barium (Ba), strontium (Sr), titanium (Ti), zirconium (Zr), copper (Cu), aluminum (Al), niobium (Nb), platinum (Pt) and ruthenium (Ru).
Consequently, it is possible to form a capacitor dielectric layer formed of a material having a high dielectric constant or a capacitor electrode formed of a metal material, by a chemical vapor deposition method.
In the method of manufacturing a semiconductor device, preferably, the organic metal complex includes a divivaloylmethane group (DPM) and a temperature of an internal wall of the vaporizing chamber is controlled to be 100xc2x0 C. to 300xc2x0 C.
Consequently, the liquid raw material can have excellent vaporizing characteristics.
In the method of manufacturing a semiconductor device, preferably, the solvent contains at least one of tetrahydrofuran and hexaphloroachiracetenate (HFA: CF3COCHCOCF3).
Consequently, the liquid raw material can have excellent vaporizing characteristics.